A page fault can carry the information of whether the access if private
or not for KVM_MEM_PRIVATE memslot, this can be filled by architecture
code(like TDX code). To handle page faut for such access, KVM maps the
page only when this private property matches host's view on this page
which can be decided by checking whether the corresponding page is
populated in the private fd or not. A page is considered as private when
the page is populated in the private fd, otherwise it's shared.

For a successful match, private pfn is obtained with memfile_notifier
callbacks from private fd and shared pfn is obtained with existing
get_user_pages.

For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
userspace. Userspace then can convert memory between private/shared from
host's view then retry the access.

Co-developed-by: Yu Zhang <redacted>
Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>
---
 arch/x86/kvm/mmu.h              |  1 +
 arch/x86/kvm/mmu/mmu.c          | 70 +++++++++++++++++++++++++++++++--
 arch/x86/kvm/mmu/mmu_internal.h | 17 ++++++++
 arch/x86/kvm/mmu/mmutrace.h     |  1 +
 arch/x86/kvm/mmu/paging_tmpl.h  |  5 ++-
 include/linux/kvm_host.h        | 22 +++++++++++
 6 files changed, 112 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 7e258cc94152..c84835762249 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h

@@ -176,6 +176,7 @@ struct kvm_page_fault {
 
 	/* Derived from mmu and global state.  */
 	const bool is_tdp;
+	const bool is_private;
 	const bool nx_huge_page_workaround_enabled;
 
 	/*

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index afe18d70ece7..e18460e0d743 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c

@@ -2899,6 +2899,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
 	if (max_level == PG_LEVEL_4K)
 		return PG_LEVEL_4K;
 
+	if (kvm_slot_is_private(slot))
+		return max_level;